Criminal insanity is a legal defense that may be used to avoid criminal responsibility. This lesson will introduce you to the concept of criminal insanity and provide examples of notable cases involving the defense as well as the tests used to determine if a defendant is criminally insane.

What is Criminal Insanity?

It's often said that the definition of insanity is doing the same thing over and over and expecting a different result. But in the context of criminal law, insanity means something entirely different. For example, insanity may exhibited by be stabbing your wife during a sleepwalking episode or trying to assassinate the president to impress a famous actress.

Criminal insanity is a legal defense used by a criminal defendant to avoid being convicted of a crime. Under this defense, the defendant must prove that he or she suffered from a mental health episode at the time the crime was committed. A mental health episode may include a mental illness, defect, or disease.

In every criminal trial, the prosecution has to convince the jury that the defendant possessed a guilty state of mind when he or she committed the crime. The insanity defense allows a defendant to prove that he or she lacked the requisite mental state to be found guilty of a crime. Without proof of a guilty state of mind, the prosecution can't prove its case!

Landmark Cases Illustrating Criminal Insanity

A pair of British cases from the 1800s are often used to illustrate the insanity defense.

In 1800, James Hadfield entered the Theatre Royal in London's West End and fired a pistol at King George III as he stood in the royal box. Although Hadfield's assassination attempt was unsuccessful, he was immediately apprehended and charged with treason.

At Hadfield's trial, his defense attorney argued that Hadfield was insane at the time of the shooting. Medical experts testified that they believed that head injuries suffered in battle rendered Hadfield incapable of understanding the criminal consequences of his actions. Hadfield was acquitted and later committed to an insane asylum.

In 1843, a Scottish woodworker named Daniel M'Naghten approached civil servant Edward Drummond on a busy London street. Without provocation, M'Naghten drew his pistol and shot Drummond in the back. M'Naghten, who believed that he was being followed by political spies, mistook Drummond for the prime minister. Drummond died five days later from his injuries.

M'Naghten was arrested and tried. At his trial, M'Naghten's defense attorneys argued that he suffered from delusions so powerful that he lacked control over his actions. After multiple medical experts testified in support of the theory of insanity, M'Naghten was acquitted. Like James Hadfield, M'Naghten lived out his days in an asylum.

One of the most famous examples of the insanity defense was featured in the trial of John Hinckley, Jr. In the early 1980s, Hinckley became infatuated with the actress Jodie Foster after watching the film Taxi Driver. As his obsession grew, Hinckley began to stalk Foster and made various attempts to contact her.

In 1981, Hinckley tried to shoot President Ronald Reagan as he left a hotel in an attempt to get Foster's attention once and for all. In his subsequent trial, Hinckley was found not guilty by reason of insanity.

Law and Defense

Over the years, courts and legal scholars have created different legal tests defining what it means to be criminally insane.

The early M'Naghten test borrows its name from Daniel M'Naghten's famous trial. Under the M'Naghten test, a defendant will be considered legally insane if a mental defect prevented him or her from understanding that his or her actions were wrong, or of the defendant did not understand the criminal nature of his or her actions.

The irresistible impulse test is generally considered to be a variation of the strict M'Naghten test. Under this standard, a defendant may assert that he or she cannot be liable for the crimes at hand because, despite knowing that his or her actions were criminal, a mental defect deprived him or her of the ability to demonstrate self-control.

A more lenient test for insanity was introduced in the 1950s in the Supreme Court's decision in Durham v. United States. The Durham test (also known as the New Hampshire test) applies when a defendant's crime is simply the product of a mental illness or defect.

The test set forth in the Model Penal Code strikes a balance between the Durham test and the M'Naghten test. Under this standard, a defendant is considered insane when a mental disease or defect diminishes his or her capacity to appreciate the criminal nature of his or her conduct, or the ability to conform one's conduct to the strictures of the law. Most modern jurisdictions apply a test similar to the Model Penal Code standard.

Lesson Summary

Criminal insanity is a defense to criminal liability. In order to assert the defense of criminal insanity, a defendant must prove that a mental defect or disease prevented him or her from forming a guilty state of mind. The defense has been a mainstay in the criminal justice system since the early 1800s.

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